No Octo while diving with redundant air supply

[rx7diver]

... What, if any, compelling reasons are there to keep the octo in play?

I don't think there is a compelling reason.

Moreover, I don't think there is a compelling reason for a solo diver to always dive with a pony bottle, depending.

Or with a PDC, for that matter--let alone with two PDC's! But now I've begun ranting ...

rx7diver

 

[NW Dive Dawg]

As a SOLO diver with a fully redundant back mounted 19cf pony, I am convinced that the best practice for me is to have an Air 2 or equivalent for the option of dual access to my primary gas......... AND have my emergency fully redundant pony 2nd on a necklace.

 

[Gandalf-the-Diver]

I think you just made the argument for a slung pony.

My slung 30cu, is always with me.

 

[johndiver999]

Where is the best place for a stage/pony?
In the front makes it more versatile. You could donate the stage - breathe from it for part of your dive and save more back gas or not breath from it and it there for back up only.

There are other advantages as well. If you should have a back mounted pony and develop a failure behind your neck, say an o-ring extrusion, LP hose failure or something less likely. How do you determine quickly and reliably when you are solo, whether it is the primary or the pony bottle that has "sprung a leak"? It may not be obvious or instantaneously distinguishable.

Another advantage is that a slung bottle will always have an spg that the diver can read and in a real emergency and on the ascent, it will be much more comforting to know your remaining gas supply, versus a back mounted pony that you are guessing about (unless you are running a redundant SPG for the pony you can read remotely or on a long spg hose).

Another advantage worth mentioning is that if you are ascending on the pony bottle and it starts to freeflow, or maybe an oring starts leaking or a hose gets a leak, you are pretty much SOL, if it is back mounted. If it is rigged as a stage, you can feather the valve on and off and drastically reduce any unnecessary gas loss.

These advantages are much more significant than the benefit of being able to "hand off" your pony bottle to the imaginary ghost diver who appears during a solo dive.

Regardless of these and other advantages, the OP is NOT slinging the bottle. He just asked about the third second stage - with a back mounted pony.

 

[Angelo Farina]

In a few occasions, I used a back-mounted pony: a 4l Alu tank in the middle of my 10+10l twin set.
The twin tank was already fully redundant, with two independent valves and two independent regs. It also had the reserve, for added gas reservoir.
When adding the pony for planned extended deco or cave penetration, I had the same doubt: moving one of two main regs from the main tank to the pony, or adding a third one for the pony?
As previously it did already happen to me to loose entirely operation from the primary reg, due to O-ring extrusion, and being able to continue the dive using the secondary reg, after closing the primary valve, I preferred to add a third reg on the pony.
And for avoiding the risk to confuse it with two main regs, I used a model with left-side hose (initially an Aquilon, which later I replaced with a rare and very good Scubapro mod. 129).
I do not think that removing one of the two main regs from the big tank is a good idea: in case of problems you loose entirely the gas trapped in it...

Said that, I did not use this setup in the last 30 years: I abandoned the twin tank in favour of a 15 liters steel single, and in case I need the pony I attach it on my side (still mounting the left-sided SP 129 on it - this always remained my "pony reg").
And when adding the pony, I make no modifications to the regs on my main tank, so I am back with three second stages: two are right-handed and come from the large tank, one is left handed and comes from the pony.

 

[Angelo Farina]

Last point.
It appears that the OP is diving solo, with a standard recreational tank and reg (single valve, one first stage only, no reserve, main secondary stage plus octopus), just adding a pony tank as "redundancy".
In my opinion this setup is absoluteluly NOT safe enough for solo diving.
My single 15 liters tank has double valve plus reserve, and I still use two fully independent regs on it.
So, considering that the original setup is not safe enough, removing the octo makes it even less safe.
For me it is wrong to remove one of the three second stages: the OP should instead add a double valve and another first stage, for enabling some redundancy on the main tank.
I concede that the reserve is nowadays difficult to find and almost obsolete, so this can be left out (despite I find it still useful).

 

[Cthippo]

I never carry an octo when diving. Not even sure I ever installed it when I got my first reg. If I am diving with someone else and they are OOA I will either give them my primary, or, if they are not panicked and we have a little time, unclip and give them my whole pony. In my opinion the benefits of a third second stage do not outweigh the costs.

 

[Cthippo]

Last point.
It appears that the OP is diving solo, with a standard recreational tank and reg (single valve, one first stage only, no reserve, main secondary stage plus octopus), just adding a pony tank as "redundancy".
In my opinion this setup is absoluteluly NOT safe enough for solo diving.
My single 15 liters tank has double valve plus reserve, and I still use two fully independent regs on it.
So, considering that the original setup is not safe enough, removing the octo makes it even less safe.
For me it is wrong to remove one of the three second stages: the OP should instead add a double valve and another first stage, for enabling some redundancy on the main tank.
I concede that the reserve is nowadays difficult to find and almost obsolete, so this can be left out (despite I find it still useful).

So, is it your opinion that a double reg failure on the same dive is a likely enough event that you need to plan for it and pay the costs to maintain the equipment to mitigate such an occourance?

 

[happy-diver]

And Winter is coming ha ah ah ah ah ahah ah ahha hqa aqhha with many extra hours to while away!

 

[Angelo Farina]

So, is it your opinion that a double reg failure on the same dive is a likely enough event that you need to plan for it and pay the costs to maintain the equipment to mitigate such an occourance?

No, a double reg failure is something I consider statistically impossible.
I am just worried that the primar reg fails (which happened to me in several occasions) and that I loose access to all the air which is trapped in the main tank.
At that point you bail out on the pony, but that is small, probably not enough for a normal return to your boat.
So you are forced to a direct vertical ascent straight up, far away from the boat, which means surfacing in a very risky condition, possibly with rough sea, wind, and uncapable to surface swim to the boat.
You are solo, so who is going to help you?
A pony is an additional safety added when diving solo, but I always want some amount of redundancy from my main tank.
I always use two separate regs for my normal rec diving (with my wife as a buddy).
And definitely I would not get rid of one of them if diving solo, which by definition is more dangerous.
A pony provides additional redundancy, but of lesser value and capacity than a dual valve large tank with two separate regs, which is my basic recreational setup.
I always considered octos "not safe enough" for me...